Generally, a medium such as an agar medium is widely used in: microbial tests in, for example, the medicinal industry and relating to GMP validation, such as a axenic test, a bacteria limiting test, an environmental falling bacteria test, a measurement of the titer (efficacy) of an antibiotic, a body fluid concentration measurement, and a preservation effect test; microbial tests in, for example, the food industry, and relating to a countermeasure of preventing contamination due to noxious bacteria based on HACCP, such as a viable cell count test, and a cell count test.
In the case where a body fluid concentration measurement of an antibiotic is to performed in the medicinal industry, for example, 5 to 10 cc of a solid medium mixed with bacteria is dispensed into a laboratory dish, and a disk or a cup is then placed on the dispensing face. Thereafter, a specimen is infiltrated or dispensed into the disk or the cup, and the specimen is cultivated. The concentration of body fluid is then measured on the basis of the size of a region where the bacteria grow.
In the case where the titer of an antibiotic is to be measured, for example, 20 cc of a base layer medium (a medium to which nutrients are added so that bacteria eat by preference the medium to rapidly grow) is dispensed into a laboratory dish and solidified therein. Thereafter, 4 cc of a seed layer medium (a medium containing bacteria) is dispensed onto the base layer medium. A disk or a cup is then placed on the surface of the seed layer medium. An antibiotic of a known titer and that of an unknown titer are dispensed into the disk or the cup at different concentrations and cultivation is then performed. Thereafter, regions where bacteria grow are measured and the titer of the antibiotic in which the titer has not been known is calculated.
Such various kinds of microbial tests are roughly classified into a qualitative test and a quantitative test. In a quantitative test, an agar medium is always used.
In such various kinds of tests, when the sampling number of a specimen is large and plural types of media are used, a very long time period is required for sampling the specimen and dispensing the media. In order to enhance the test accuracy, the work of dispensing a medium must be performed in a sterilized room or the like.
An apparatus for automatically performing sampling of a specimen and the work of dispensing a medium is disclosed in, for example, Japanese Unexamined Patent Publications (Kokai) Nos. Hei. 5-153961, Hei. 4-248980, and Hei. 3-49676.
FIG. 20 is a view schematically showing the configuration of a medium dispensing, mixing and diluting apparatus 200. The dispensing, mixing and diluting apparatus 200 comprises a medium dispensing apparatus 201 which dispenses a medium material, and a mixing and agitating apparatus 202 which mixes and dilutes the medium material, and mixes a specimen diluent 203 with an agar medium 204 to automatically prepare a poured culture plate.
In the dispensing, mixing and diluting apparatus 200, first, empty laboratory dishes 206 which are accommodated in a vertical stacked state are extracted one by one from a rack 212, and sent onto a conveyor which is not shown, to be transported. With respect to each of the laboratory dishes 206 which are transported by the conveyor, a lid is opened and the specimen diluent 203 is then dispensed into the laboratory dish by a specimen diluent dispensing apparatus 209. The specimen diluent dispensing apparatus 209 sequentially dilutes the specimen in a test tube at plural steps of dilution ratio with a diluent, and dispenses the specimen diluent 203 into the laboratory dish 206 by means of a micro pipette 210.
Next, the medium dispensing apparatus 201 supplies a preset amount of the molten agar medium 204 from a medium dispensing nozzle 205 into the laboratory dish 206, via a medium tank (not shown), a circulation pipe (not shown), and a manifold (not shown).
In the mixing and agitating apparatus 202, an agitation plate 207 is rotated by a rotation mechanism 208, whereby the specimen diluent 203 which has been dispensed into the laboratory dish 206 by the specimen diluent dispensing apparatus 209, and the agar medium 204 which has been dispensed into the laboratory dish 206 by the medium dispensing apparatus 201 are mixed with each other and agitated. The specimen diluent 203 and the agar medium 204 which are mixed together are solidified by a cooling apparatus 211 to prepare a poured culture plate. Thereafter, the lid is put on the laboratory dish 206, and the laboratory dish is then accommodated in a rack 213 in a vertical stacked state.
Therefore, the above-described dispensing, mixing and diluting apparatus 200 can mix the specimen diluent 203 and the agar medium 204 at a given amount with each other and automatically prepare a poured culture plate. It is a matter of course that, when the step of dispensing the specimen diluent 203 is omitted and only the agar medium 204 is dispensed, it is possible to prepare a plate medium.
The dispensation and mixture and dilution of a medium are processed in different manners depending on the kind of a test in which the medium is used, and roughly classified into medium dispensations of four kinds, a plate medium, a poured culture plate, a multilayer medium, and a thin layer medium. A mixing and diluting step of mixing and agitating a specimen diluent and an agar medium is conducted only in preparation of a poured culture plate.
For a plate medium and a poured culture plate among the media, the above-described dispensing, mixing and diluting apparatus 200 can be used An dispensation and mixture and dilution. With respect to dispensation of a multilayer medium and a thin layer medium, however, the above-described dispensing, mixing and diluting apparatus 200 cannot perform automatic dispensation because the amount of the dispensed medium is small and the dispensed medium hardly spreads.
Specifically, in dispensation of the multilayer, the dispensation amount of the medium of the seed layer to be stacked is small (for example, about 4 cc), the medium hardly spreads in a uniform manner during dispensation, and the temperature of the base layer which is previously solidified is lowered to the vicinity of room temperature (usually, 20 to 24.degree. C.). After dispensation, therefore, the medium must be promptly spread in a uniform manner.
In dispensation of the thin layer medium, because the dispensation amount of the medium is small (for example, about 5 cc), and the surface of a laboratory dish has water repellency owing to a silicone release agent which is used in molding of a plastic laboratory dish, there is a problem in that the medium hardly spreads in a uniform manner during dispensation.
Also with respect to dispensation and mixture and dilution of the plate medium and the poured culture plate, in the above-described dispensing, mixing and diluting apparatus 200, the fluidity is insufficient depending on the concentration of a medium on a laboratory dish, whereby a problem of reduced smoothness of the medium may be caused. When the temperature of a medium is kept high, the fluidity of the medium can be maintained so that even a small amount of the medium can be dispensed. When a medium is heated to 50.degree. C. or higher, however, bacteria of the specimen die. During the work of dispensing or mixing and diluting a poured culture plate, a multilayer medium, and a thin layer medium, therefore, the temperature of a medium cannot be kept high so as to maintain the fluidity of the medium.
To comply with this, in the dispensing, mixing and diluting apparatus 200 of the conventional art, dispensation and mixture and dilution of a plate medium and a poured culture plate, and dispensation of a multilayer medium and a thin layer medium in which a small amount (for example, less than 7 cc) of the medium is used cannot be automated. Consequently, the dispensing work must be manually performed, thereby producing a problem in that it requires a great deal of labor and time.
Therefore, it is an object of the invention to provide a medium dispensing apparatus which can solve the above-discussed problems, in which, even when a small amount of a medium is to be dispensed, the medium can be satisfactorily dispensed, and an uneven thickness of the medium and the like can be surely prevented from occurring, and which can be satisfactorily used in dispensation of any of a plate medium, a poured culture plate, a multilayer medium, and a thin layer medium, and also a method for the same.